Mosquito-transmitted parasitic diseases are among the major causes of mortality and morbidity in the world. Female mosquitoes require a blood meal in order to obtain the nutrients for egg production. The act of taking the blood meal is the point at which the mosquito transmits parasitic diseases. The long-term objective of this project is to attain a better understanding of blood meal digestion; this information could be the basis for the development of new mosquito control strategies. Ingestion of the blood meal induces the synthesis of two female-specific trypsin; early and late trypsin. Early trypsin is induced in small amounts within the first 4-6 hours following the blood meal. The regulation of early trypsin synthesis is at the post-transcriptional level: its mRNA accumulates in the midgut following adult emergence, but translation occurs only after ingestion of a blood meal. Early trypsin is a "sensor": the enzymatic activity of early trypsin is an obligatory component of the signaling system that activates the synthesis of the late trypsin; this second protease is produced in large amounts 8-24 hours after feeding, and is the major endoproteolytic enzyme responsible for the digestion of the blood proteins. The regulation of late trypsin synthesis is at the transcriptional level. The fundamental role of midgut trypsins in egg production and parasite transmission underscores the need for a more detailed understanding of the regulation of trypsin gene expression. In order to characterize these processes further, the following specific aims are proposed; A) to investigate the role of juvenile hormone and other factors in the regulation of early trypsin transcription; B) to determine the mechanism of the regulation of translation of the early trypsin mRNA by feeding; C) to identify the products of early trypsin proteolysis of the blood meal which induce the activation of the late trypsin gene; and D) to identify and characterize cis-acting regulatory elements in the late trypsin gene which are involved in regulating expression of the gene.